Z Elem Known Stable Unstable Pred. Gap Nuclear γ (keV) NIST Kα₁ (keV) Context 61 Pm 39 0 39 93 54 — 38.707 No stable isotopes; XRF line 62 Sm 41 7 34 97 56 333.0 40.093 ¹⁵³Sm therapy + XRF 63 Eu 40 2 38 95 55 121.8 / 344.3 41.507 ¹⁵²Eu calibration + … Continue reading Master Isotope Table — NIST SRD-128 Kα₁ (Z = 61–80)